A single antenna aperture that can simultaneously cover multiple bands with proper polarization is highly attractive since this greatly simplifies system complexity and cost. For example, distinct frequency bands (e.g., K- and Ka-frequency bands) often times together form an important and popular downlink/uplink pairing. From the perspective of a ground terminal, the polarization assignment for these bands is typically left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), respectively.
Polarizers can take on many forms and functions. In frequency spectrums where linear polarization dominates (e.g., Ku-band), a commonly used polarizer is the twist polarizer which takes an input linearly-polarized wave in one direction and twists it to a differently oriented (but still linear) polarization. A different type of polarizer is the meanderline polarizer which converts an input linearly polarized wave to circular polarization.
There are several existing approaches to providing dual orthogonal polarization outputs from a common shared aperture. A popular solution for dish/reflector-type antennas is to employ a circular feed horn together with an orthomode transducer. This dish setup outputs two orthogonal linear channels, which can be phased to receive/transmit LHCP or RHCP for that band. A second feed horn illuminating the same common dish/reflector can provide additional coverage in another band. Similar implementations exist for other transmission mediums (i.e. dual aperture-coupled patch) but these all operate on the same principle of providing dual orthogonal output channels. A meanderline polarizer placed at the output of these apertures can convert these two orthogonal linearly polarized waves into separate orthogonal RHCP and LHCP signals.
However, each of these existing arrangements require antennas that support two orthogonal polarizations. What is needed is a polarizer that can instead operate on just a single polarization, greatly reducing system complexity and costs. In the K/Ka downlink/uplink frequency spectrums, for example, such a polarizer needs to convert an input linearly polarized electromagnetic wave to one sense of circular polarization (CP) (e.g, LHCP) in the first band and the opposite sense of CP (e.g. RHCP) in the second band.